1. Field of the Invention
The present invention relates to a multilayer ceramic electronic component and a manufacturing method thereof. In particular, the present invention relates to a multilayer ceramic electronic component in which an external terminal electrode is coupled not only to an exposed end of an internal electrode but also to an exposed end of a dummy conductor so as to improve the fixing strength of the external terminal electrode, and a method for manufacturing such a multilayer ceramic electronic component.
2. Description of the Related Art
In recent years, electronic apparatuses, such as cell phones, notebook personal computers, digital still cameras, and digital audio systems have been downsized. These electronic apparatuses use many downsized, high-performance, multilayer ceramic electronic components.
Generally, a multilayer ceramic electronic component includes a ceramic element including a plurality of ceramic layers laminated on each other, internal electrodes provided inside the ceramic element, and external terminal electrodes provided on an outer surface of the ceramic element. The multilayer ceramic electronic component is disposed on a conductive land of a mount substrate and mounted on the substrate with a conductive bonding material, such as solder, interposed therebetween.
Currently, multilayer ceramic electronic components are required to be further downsized. If multilayer ceramic electronic components are further downsized, the opposed effective areas of the internal electrodes are reduced. This degrades the characteristics. In addition, for a multi-terminal multilayer ceramic electronic component, a plurality of strip external terminal electrodes must be arranged at relatively small pitches. If a typical method of printing a thick film paste is used, there is a limit to the accuracy of the paste application. Therefore, it is difficult to form external terminal electrodes with high accuracy.
In view of the foregoing, a method of forming external terminal electrodes by direct plating has been developed. This method enables the formation of thin, flat external terminal electrodes. The effective areas of the internal electrodes are increased accordingly. In addition, since plating is deposited at the exposed ends of the internal electrodes, external terminal electrodes can be accurately formed even at small pitches.
For example, Japanese Unexamined Patent Application Publication No. 2004-327983 discloses that when external terminal electrodes are formed by direct plating as described above, dummy conductors that do not substantially have electrical characteristics are used. Thus, plated metal will be deposited not only at the exposed ends of the internal electrodes but also at the exposed ends of the dummy conductors, and thus, the plating will grow more reliably.
If a multilayer ceramic electronic component including dummy conductors as described above is manufactured, internal electrode patterns and dummy conductor patterns are printed on ceramic green sheets and the ceramic green sheets are laminated and crimped on a sheet-by-sheet basis, and a mother block formed thereby is pressed.
As shown in FIG. 14, in the lamination and sheet-by-sheet crimping process, a ceramic green sheet 10 is transported to a press base 11 by a press head 9, and the ceramic green sheets 10 are successively laminated and crimped on the press base 11. Here, a plurality of ceramic green sheets 10 to be included in a mother block are laminated and crimped sequentially from the bottom. Therefore, the crimping load is repeatedly applied to the ceramic green sheets 10 that are laminated earlier and the conductor patterns such as internal electrode patterns and dummy conductor patterns. In particular, pressure is applied to a greater extent to high-density portions of the above-mentioned conductor patterns. This causes the conductor patterns on the lower main surface of the mother block, which is a surface near which the ceramic green sheets 10 that are laminated earlier are located, to become larger than the conductor patterns on the upper main surface thereof.
This phenomenon is problematic particularly when forming external terminal electrodes by direct plating. Specifically, if the conductor pattern on the lower main surface is extended, differences occur between the widths of the exposed ends of the internal electrodes or dummy conductors near the upper main surface of the ceramic element and the widths of those near the lower main surface thereof. These differences cause a problem in that the external terminal electrodes 12 have a trapezoidal shape, as shown in FIG. 15. FIG. 15 shows a side surface 14 of a ceramic element 13 on which the plurality of strip external terminal electrodes 12 are formed.
If the external terminal electrodes 12 have the trapezoidal shape as described above, a problem occurs in that a tombstone failure or a self-alignment failure occurs due to the directionality of the vertical direction or a problem occurs in that a solder bridge is likely to occur at the lower sides of adjacent trapezoidal external terminal electrodes 12.